Development and Integration of Earth System Model Components

A continuing task of the Program is to improve and extend the capabilities of its Earth System Model (the IGSM), which links the climate system (atmosphere, ocean, and terrestrial process) to the human drivers of global change and to system responses to climate and other environmental impacts. There are substantial feedbacks among these processes, and they matter for informing the design of mitigation efforts and understanding economic and environmental risks. The research task is necessarily multi-disciplinary and requires close participation of researchers with expertise in atmospheric and oceanic modeling, analysis of soils, terrestrial hydrology and vegetation, atmospheric chemistry and modeling of economic and technological options.

Research on the critical role of non-CO2 greenhouse gases and other radiatively important substances has been influential in research and policy formulation. Program research highlighted the mitigation costs savings possible through a broad policy that included multiple greenhouse gases, which was the first integrated science and economic analysis of the issue that emphasized the importance of a multi-gas approach.

The Program's work has strongly shaped international and U.S. policy through publications such as Multi-gas contributors to global climate change: Climate impacts and mitigation costs of non-CO2 gases. At the same time this work has questioned the adequacy of Global Warming Potential indices, especially their potential to underestimate the value of controlling methane (Stabilization and global climate policy). Recent work has been a motivation for programs such as the U.S. Methane for Markets, emphasizing that substantial climate benefit can be achieved if global methane emissions are curbed even as nation's continue the difficult negotiations on limiting CO2.

While key non-CO2 greenhouse gases have been now widely recognized in policy approaches from climate mitigation, the consideration of other substances also important in the climate issue has been less fully incorporated. Research in the Program has highlighted the critical role of urban air pollution processes on the formation of ozone. Research has also focused on the critical role of aerosols in the climate issue, identifying their potential to substantially shift precipitation patterns..

Other Program work showed that increased ozone levels would damage vegetation, thereby reducing carbon uptake by ecosystems, making it substantially more costly to achieve a given atmospheric CO2 "stabilization" target. Ozone also has strong effects on agricultural productivity (Global economic effects of changes in crops, pasture, and forests due to changing climate, carbon dioxide, and ozone), which feeds back on climate itself.

The Integrated Global Systems Model (IGSM) developed within the Program is among a class of models that have come to be known as Earth System Models of Intermediate Complexity (EMICs). Work at the Program and a few other centers around the world has largely defined this class of models and their use. These models are designed to represent underlying processes of the Earth system, but to remain computationally efficient and to retain flexibility to represent the range of responses of key Earth system parameters that are consistent with observations. The broad acceptance of this class of models, and their role in understanding Earth system processes, is now well-established as evidenced by the inclusion of their results in the reports produced by the Intergovernmental Panel on Climate Change (IPCC). The computational efficiency of these models makes it possible to use them effectively to run large ensembles of future projections, to be used in detection and attribution work, and as decision support tools, such as in the U.S. Climate Change Science Program Report on new emissions scenarios.